1. Field of the Invention
The present invention relates to a control system for a high-speed multihead weigher, sometimes called simply a weigher. The multihead weigher is a combinatorial weighing system composed of a series of completely independent weighing modules, called heads, connected to a so called central control unit, composed of a common personal computer (PC) or the like, by means of a low-speed serial network.
2. Description of the Related Art
Generally a combinatorial weighing system is composed of a set of identical modules, each equipped with its own vibrating channel, a loading bucket, a weighing bucket coupled with a load cell or the like and may include a memory bucket. A typical realization of a combination weighing system foresees that these modules are placed according to a circular configuration, even if also other types of configurations are possible, for example a rectilinear one. As will be understood by those skilled in the field of combinatorial weighers, in case of circular configuration the product or articles is delivered radially starting from the machine center, the buckets of each module are filled and the product in the weighing buckets is weighed. The combination of the weights contained in the weighing buckets of the modules that comes closest to the required weight is discharged in a transfer device, for example a cone or a funnel, which conveys the product towards a packaging system.
The electromechanical members with which each module is equipped are the motors for the motion of the buckets, the electromagnets in order to drive the vibrating channels and the load cells to weigh the product inside the weighing buckets. In order to describe the prior art in relation to the control of these electromechanical devices two complementary solutions will be mentioned.
U.S. Pat. No. 4,694,920 to Naito et al. relates to a combinatorial weigher having a control system composed of at least three central processing units which control respectively the acquisition of the electric signals coming out from the load cells (said weight-monitoring section), the devices for the motion of the product to be weighed such as motors and vibrating feeders (said drive-control section) and the digital signals for the selection of the weights combination to be discharged (said main section). As the electromechanical members are distributed on a circular structure whose dimensions are not negligible, there is an evident necessity to reach said devices with some cables starting from a unit which is physically dislocated far from them. The cables are the cause of an increase of the general system costs and are a potential source of malfunction due to possible disconnections. Besides, the presence of cables, whose length is not negligible, for the feeding of motors and electromagnets generates electromagnetic interferences, which can cause malfunctions of the electronic systems incorporated in the machine, as partially pointed out in the U.S. Pat. No. 4,658,919 to Nobutsugu.
U.S. Pat. No. 5,981,881 to Kawanishi et al relates to another architecture, wherein the control system of the machine is composed of a single weighing control unit which is connected through a high-speed local area network (LAN) to the weighing modules. Each module contains some electromechanical members with relative electric drivers and interfaces itself with the LAN through a LAN interface. In this case the previously mentioned problems that accompany use of cables, namely (1) increased cost (2) malfunction due to possible misconnections, and (3) presence of electromagnetic interference, do not exist. However, if a LAN is used, it needs to be a high-speed LAN because the weighing control unit can manage all the weighing modules and can therefore respond quickly to data such as operating conditions or control information between the weighing control unit and the weighing modules. When the number of weighing modules and the machine speed (weights/minute) increase, the quantity of information exchanged between the generic control unit and the peripheral modules increases considerably. In order to allow to the central unit a rapid control of the peripheral members such as motors, vibrating channels, load cells, etc., it is necessary to use a high-speed communication network, such as a LAN. The patent states that the use of a high-speed LAN allows the upgrade of software memorized in the modules control electronics. The prior art mentioned in this patent states clearly that, if the weighing driving sections are connected to the weighing control unit through an ordinary serial telecommunication line, it is impossible for the weighing system to reach high operating speed in terms of weights/minute.
The use of a high speed LAN reveals itself expensive if compared to the simplest serial asynchronous low-speed communication lines used for example in a common PC or similar apparatus. In a typical industrial environment the electromagnetic pollution level is rather high and the presence of electromagnetic interferences can considerably reduce the reliability of a high-speed communication system such as a LAN, causing an increase of the error probability. In general the more such decrease in reliability is marked, the higher the transmission speed of the data. In particularly demanding situations the lack of a reliable link between the central unit and the peripheral modules of the weigher, because of frequent communication errors, can determine an undesired reduction of the weigher working speed. The patent also discusses insertion of electro-optical converters in the communication interfaces, or in the introduction of optical fiber sections inside the network. However, this results in an increase in the hardware complexity and a further increase of costs.
In order to manage a combinatorial weigher there is the necessity of some fundamental functional blocks or electronic subsystems, such as a unit for the calculation of the combinations, a graphic or alphanumerical unit for the input/output of data, a section for the storage of data and programs and a communication interface with the weighing peripheral modules. In some cases these electronic subsystems are placed in different points inside the weigher, while in other cases instead they are dislocated and interconnected with each other in a single housing of the weigher called central control unit. The central control unit is therefore generally composed of a multiplicity of electronic subsystems conceived as intrinsically independent, with definite and separate functions, which together carry out the requested control functions. The disadvantages of such a custom-made architecture appear evident if the possible cost reductions and the decrease of structural complexity are considered. This approach results in high costs due to the design and manufacture of separate subsystems, and loss of reliability due to possible misconnection of the subsystems.
Also the weighing modules are characterized by a set of electronic subsystems such as motor drivers, vibrating feeders electromagnet drivers, calculation digital units and communication interfaces. A critical point as far as the reliability of the weighing modules is concerned consists in a considerable quantity of cables which interconnects the mentioned electronic subsystems. These connections raise the cost of a weighing module and can determine malfunctions due to accidental disconnections.
Often there is the problem of integrating a weighing system in the factory network that controls the industrial plants. Sometimes the possibility to monitor or control a weighing system from a geographically remote place is requested. The above mentioned custom-made control units are generally not set up for this type of application and need hardware expansion modules such as modem or additional LAN interfaces, with consequent increase of the costs and of the system hardware complexity. Also, communication through telephonic public network between the central control unit and a remote controller located in perhaps a different country or continent has often very high costs. For this reason the control and monitoring functions of one or more weighing systems from a geographically remote place cannot be active for an indeterminate time.
In order to address the above mentioned problems of the prior art, it is an object of the present invention to provide a combinatorial weighing high-speed system, said multihead weigher, comprising a PC or the like that carries out all the functions of a central control unit and which is connected to the weighing peripheral modules only through its own low-speed serial port.
Each weighing peripheral module is run by its single board weighing module controller installed near the electromechanical members of the head. The single board weighing module controllers are connected to each other only through a low-speed serial network linked to the serial port of the central control unit.
The invention addresses the problem stated in the prior art that correlated the maximum working speed of a combinatorial weigher with the transmission speed of the communication network. The use of a high-speed LAN or the like is not necessary due to the implementation of a finite state machine, sometimes called automaton, on each single board weighing module controller.
Such finite state automatons, are able to process the macro-commands sent by the central control unit to the single board weighing module controller through the low-speed serial network. The necessity of a high transmission speed is not needed because with a single macro-command it is possible to let an automaton of a generic single board weighing module controller carry out a sequence of separate operations, which as alternative would have been carried out individually, each answering to a specific command of its own transmitted by the central control unit to the generic weighing control unit. The low transmission speed of the data added to the simplicity of the hardware used for the communication allows a relevant reduction of costs and provides an excellent reliability of the transmission even in the presence of strong electromagnetic interferences.
The use of an architecture composed of a plurality of single board weighing module controllers, each placed near the relative electromechanical members to be driven and connected through a common low-speed serial network to the central control unit in daisy chain configuration, allows the minimization of the number of electric connections present in the multihead weigher. The minimization of the number of electric connections has, as favorable consequences, a relevant reduction of costs, an increase of the system intrinsic reliability, as well as a decrease of the electromagnetic emissions associated to the cables for the feeding of motors and electromagnets. The number of the weighing modules run by the central control unit can be easily increased by simply connecting further weighing modules to the low-speed serial network.
The use of a PC or the like in order to carry out the functions of a central control unit allows to realize a control system which integrates in a single electronic card the unit for the calculation of the combinations, a driver for an LCD monitor or the like equipped with a touch-screen graphic interface for the input/output of the data, the data storage unit and the low-speed asynchronous serial port. Such architecture addresses the problems mentioned in the prior art. The presence of a PC or the like as a multihead weigher central control unit allows its connection to Internet for the remote control on a world scale at low costs. Therefore, the multihead weigher could be permanently connected, 24 hours a day, to Internet for aims of remote control, of production data monitoring or remote assistance by the manufacturer.
To be able to have a PC or the like as a central control unit allows the multihead weigher to be easily connected to a local computer system for the management of an industrial plant, such as a factory network, and therefore, for example, to be able to control a plurality of multihead weighers from a single control room, which is often desired or required in weighing and packaging plants.
Having a PC or similar apparatus, realized with a single electronic card and conceived for industrial control applications, allows a modem for easy connection to a public communication network (fixed or mobile) and an interface for the connection to a computer network.
According to one aspect of the invention, a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a central control unit connected to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one macro-command, wherein each of said weighing module controllers controls its weighing module to perform article weighing, discharge and refill operations in response to said at least one macro-command, to thereby reduce the number of commands issued from central control unit to the weighing module controller which would otherwise occur without the macro-command.
According to another aspect of the invention, a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a central control unit connected over a low speed serial network to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one macro-command, wherein each of said weighing module controllers controls its respective weighing module to perform article weighing, discharge and refill operations in response to said at least one macro-command, to thereby reduce the number of commands issued from central control unit to the weighing module controller which would otherwise occur without the macro-command.
According to another aspect of the invention, a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, each weighing module controller consisting essentially of a single board.
According to another aspect of the invention, a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a general purpose computer connected to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one macro-command, wherein each of said weighing module controllers controls its weighing module to perform article weighing, discharge and refill operations in response to said macro-command, to thereby reduce the number of commands issued from central control unit to the weighing module controller which would otherwise occur without the macro-command.
According to another aspect of the invention a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a central control unit connected to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one command, wherein each of said weighing module controllers controls its weighing module to perform article weighing, discharge and refill operations in response to said at least one command, and a remote control unit, connected to the central control unit, for controlling the issuance of at least one command from the central control unit.
According to another aspect of the invention a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a central control unit connected to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one command, wherein each of said weighing module controllers controls its weighing module to perform article weighing, discharge and refill operations in response to said at least one command, and a remote control unit, connected to the central control unit over Internet, for controlling the issuance of at least one command from the central control unit.
According to another aspect of the invention, a control system for a combinatorial weigher system is provided, comprising a plurality of combinatorial weighers, each comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a central control unit connected to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one command, and wherein each of said weighing module controllers controls its respective weighing module to perform article weighing, discharge and refill operations in response to said at least one command, and wherein one of said central control units of said plurality of combinatorial weighers is a supervisor control unit which controls the remaining central control units of the plurality.
According to another aspect of the invention, a control system for a combinatorial weigher is provided, comprising a plurality of weighing modules, each weighing module receiving articles to be weighed, each weighing module comprising a weighing module controller for controlling article weighing, discharge and refill operations of its weighing module, a central control unit connected to the plurality of weighing module controllers for controlling the weighing module controllers by issuing at least one command, wherein each of said weighing module controllers controls its weighing module to perform article weighing, discharge and refill operations in response to said at least one command and.a remote control unit, connected to the central control unit, for controlling the issuance of at least one macro-command from the central control unit.
According to another aspect of the invention, a control system for a combinatorial weigher is provided, comprising an article weigher for weighing articles and forming articles into batches to be packaged, a feeder for supplying articles to be weighed to the article weigher, a packing station for packing the batches of weighed articles into packages, a packer interface for controlling the supply of articles supplied by the feeder to the article weigher and for controlling delivery of the batches of weighed articles from the article weigher to the packing station, and a central control unit connected to said packer interface through a low speed serial network, said central control unit issuing to said packer interface at least one command indicating the delivery to the packing station of a package to be filled, in response to which command the packer interface controls delivery of a batch of weighed articles to the packing station.
Other objects and advantages will appear from the following figures, detailed description and appended claims.